Performance analysis of fined pipe in air sampling smoke detection system at refrigerated warehouse

Abstract

Refrigerated warehouse is temperature-controlled environment that contain a wide range of frozen foods and dry items. However, in situation of fire, fire is rapidly spread coupled with a dry environment and high airflow by air condition system. Therefore, to minimize damage and loss in refrigerated warehouse, a fire must be detect at a very early stage. Generally, air sampling fire detection system is widely used in refrigerated warehouse. The air sampling fire detection system sampled cold air with smoke via pipe network located the underside of the ceiling. The cold air flows into laser-smoke detector chamber installed at outdoor. However, temperature of the detector chamber falls below the dew point by cold air, condensation and frosting occur and cause malfunction. Therefore, in order to prevent condensation and frosting, aluminum fin and pipes are designed to raise the temperature above the dew point. Especially, the average temperature and humidity of summer in Korea is 30℃ and 70%. Thus, the dew temperature at summer is about 21 ℃. In this study, numerical analysis is performed to investigate heat transfer characteristics according to the number of fins. The number of fins are varying 0, 2, 4 and 8 respectively. The inlet temperature of air is – 19 ℃. The pipe diameter is 10 mm and 2.5mm thickness. The geometry of fin is 22.5mm length, 1mm thickness. Also, the fin efficiency of finned pipe is compared to the bare pipe. As a result, temperature of outlet air are -3.14 ℃, -1.35 ℃, 0.1 ℃ and 2.16 ℃ and fin efficiency are increases 0.34, 0.37 and 0.41, according to the number of fins are varying 0, 2, 4 and 8 respectively. The condensation occurs when temperature is lower than dew temperature. Therefore, to satisfy the outlet temperature above the dew point, the number of fins and pipes must be increased, but the number of fins cannot be increased further due to machining and installation problems. Therefore, to increase the temperature of the outlet over the dew point, an additional heating method is required.